Can RSI Assess Neuromuscular Fatigue?

Last time out we looked at the potential for using jump testing to monitor neuromuscular fatigue. To summarise briefly, the countermovement (CMJ) jump shows strong promise as an assessment tool. The flight time to contraction time (FT/CT) ratio during the CMJ appeared to be the measure most sensitive to change following a fatiguing event.

What’s the problem with FT/CT?

To work out contraction time during the CMJ you’ll need a force plate. Do you have a force plate? If so, great. If not, we need to start looking at potential alternatives.

What is FT/CT meant to represent?

The FT/CT is representative of the movement strategy utilised to perform the CMJ. A longer CT (i.e. slower speed of contraction) indicates utilisation of a slower jumping which may indicate neuromuscular fatigue.

Enter the RSI…

RSI stands for reactive strength index and can be determined during a drop jump using a simple contact mat. The RSI is a function of either:

flight time / ground contact time

jump height / ground contact time

Personally, I’ll always favour the former. It’s possible to calculate jump height in a plethora of different ways so think it avoids a little confusion.

What does the RSI represent?

The RSI gives provides an indication of an athlete’s capacity to utilise the stretch shortening cycle in similar manner to the FT/CT. A longer ground contact time is indicative of a longer contraction time and, as with the FT/CT, highlights the utilisation of a slower jumping strategy.

Added impact?

An advantage the RSI has over the FT/CT is that it also demonstrates the capacity to tolerate impact loading, a parameter which also may be sensitive to fatigue. Indeed, a study by Nicol et al. (1991) published in the very first issue of Scandinavian Journal of Medicine & Science in Sports reported an increase in impact forces during a drop jump performed following a fatiguing marathon run.

Why is it a potential monitoring tool?

The roots of using the RSI as a monitoring tool can largely be traced back to an investigation by Oliver et al. (2008). Oliver et al. examined changes in the jump performance of youth footballers (aged: 15.8 ± 0.4) following a sport-specific exercise test. Squat jump (-1.4 ± 1.6 cm; P < 0.05), CMJ (-3.0 ± 2.9 cm; P < 0.05) and drop jump (-2.3 ± 1.7 cm; P < 0.01) performance were all impaired by fatigue, however, the only force variable to be affected was impact loading in the drop jump.

Is the drop jump better than the CMJ?

Two studies by Dave Hamilton may shed light on this question. Initially it was reported that CMJ height was not affected during a period of intensified completion in elite youth (aged: 14.4 ± 0.4) soccer players (Hamilton 2009a). A subsequent study in a similar population went on to demonstrate that drop jump RSI appeared to provide an indication of neuromuscular fatigue when examined on an individual, but not group, basis (Hamilton 2009b).

Who is using the RSI as a monitoring tool?

The popularity of the RSI as a monitoring tool hit new heights in 2012. The UKSCA conference of that year was littered with references to how this was incorporated by the English Institute of Sport, perhaps most notably in Dave Hamilton’s presentation on the physical preparation of the GB women’s field hockey team in the years leading up to 2012 (Hamilton 2012). The data he presented certainly appeared to back up his previous observations in youth soccer.

Is RSI monitoring viable?

Given the relatively low-cost and additional utility of jump mats, RSI monitoring is now a viable option for almost all professional organisations and a considerable percentage of sports teams.

But is RSI all it’s cracked up to be?

A new study to be published in an upcoming issue of the European Journal of Sport Science sought to evaluate both the short- and long-term potential of jump based monitoring. Oliver et al. (2015) evaluated the CMJ height, RSI, leg stiffness and perceived well-being of elite junior (aged: 16.9 ± 0.8) rugby players over a seven-week in-season period. Unsurprisingly, the authors reported that CMJ, RSI and well-being were all sensitive to detecting post-match fatigue. However, whereas CMJ and stiffness were deemed sensitive to detecting accumulated fatigue over the seven-week period, RSI and well-being were not.

It’s important to note that the RSI in the Oliver study was not measured during a drop jump, but during a series of repeated CMJs. This technique typically results in a less reliable measurement and may explain why such a substantial variation was observed in the study.

Hopefully the last two posts have given you an insight into the rationale behind using jump based monitoring. Next time out I’ll walk you through my own thoughts and observations. I’ll promise you’ll not have to wait as long as last time for this one!

References:

Hamilton D. Drop jumps as an indicator of neuromuscular fatigue and recovery in elite youth soccer athletes. Journal of Australian Strength and Conditioning. 2009: 17: 3-8.

Hamilton D. Explosive performance in young soccer players during several games in succession: a tournament scenario. Journal of Australian Strength and Conditioning. 2009: 17.

2 comments

Hi there,
Just a few questions…. How is contraction time different to contact time?
Can a jump mat (not force plate) measure contraction time?
Is contraction time/ flight time ratio only useful using a drop jump protocol?

Contraction time is estimated from the force trace so needs a force plate. Essentially, the contraction time starts when the athletes starts to dip and ends when the athlete takes off. Contraction time can therefore be used in CMJ and DJ, contact time can only really be used in DJ.
Mats only tell you when the athlete is on/off the mat. So you couldn’t determine contraction time in a CMJ but contraction time and contact time should be similar in DJ.
I think DJ tests are more sensitive to fatigue-based changes than CMJ.